The present invention relates to a fan impeller designed for fans of cooling towers with fan blades that are made of fiber-reinforced plastic material. The fibers extend substantially parallel and/or at an acute angle to the longitudinal axis of the fan blade and are designed to transmit the forces that collectively act on the fan blades into the impeller hub. The reinforcement fibers at the radially inwardly positioned end of the fan blades are bundled to form a tubular structure and are connected to the hub by fastening rings that engage the outer surface and the inner surface of the tubular structure so as to be rotatable about the longitudinal axis of the fan blade.
Fan impellers of the aforementioned kind are known in various embodiments. In these known constructions the tubular structure of the bundled reinforcement fibers at the radially inwardly positioned end of the blade is widened and into the widened interior a conical inner ring is inserted that together with a conical exterior ring by a wedging action on the fiber bundle clamps the fiber bundle so that the forces acting collectively on the fan blades are transmitted onto the impeller hub.
This known construction has not only the disadvantage of a great axial extension of the clamping elements, but also, depending on the wedging angle, results in a relatively high load of the reinforcement fibers, especially on those located in the area of the inner and outer surfaces of the tubular fiber bundle.
It is therefore an object of the present invention to provide a fan impeller of the aforementioned kind such that, on the one hand, the axial constructive length for the clamping of the tubular fiber bundle is shortened and, on the other hand, the constructive expenditure for the fastening of the reinforcement fibers at the fastening elements as well as for the arrangement of the fastening elements at the impeller hub is reduced to thereby lower the manufacturing costs.